Phosphor-converted LED devices having improved light distribution uniformity

ABSTRACT

A New Phosphor-converted LED Device (“NPCLD”) is disclosed. The NPCLD may include a lens over a phosphor body, in which the lens and the phosphor body each have a substantially convex upper surface. The NPCLD may alternatively include first and second lenses, the first lens having a substantially flat interface with a phosphor body.

BACKGROUND OF THE INVENTION

Phosphor-converted light emitting diode (“LED”) devices are useful forgenerating light output having actual and perceived spectralcharacteristics that differ from the actual spectral characteristics ofthe LEDs themselves. For example, the advent of blue LEDs was a keydevelopment in the quest for LED devices emitting apparently whitelight, as potential replacements for incandescent and fluorescent bulbs.Blue LEDs have been integrated with yellow phosphors to emit blue andyellow photons in ratios that are perceived by the human eye as whitelight. Although these photonic emissions do not span the completevisible spectrum and therefore are not actually equivalent to sunlight,they appear to be white and thus may be effectively utilized, forexample in lighting applications. Since LED devices may convertelectricity into photonic emissions more efficiently than incandescentand fluorescent bulbs, the potential benefits of LED use for lightingand other applications in terms of energy conservation are great.Further, as solid state devices, LED devices have a larger averagelifetime of use than and often are more resistant to physical damagethan are conventional incandescent and fluorescent bulbs.

Phosphor-converted LED devices typically emit photons having at leasttwo discrete wavelengths, which are generated by at least two differentsources that are located close to, but not in identical positions as,each other. One source is electroluminescent radiation from the LEDitself; another is luminescent radiation from the phosphor, asstimulated by radiation from the LED. Unfortunately, the non-unity ofboth the physical positioning and the functional operation of thesephotonic sources generally results in non-uniformity in the additivephotonic emissions from conventional phosphor-converted LED devices,producing an unwanted wide white color bin spread.

As an example, the structure of a conventional phosphor-converted LEDdevice may include an LED that is overlaid by a selected phosphor. In anexample of operation, the electroluminescent emissions from the LED atone wavelength are partially intercepted by the phosphor, resulting instimulated luminescent emissions from the phosphor that are usually at alonger wavelength. Photons emitted by the LED at a first wavelength andby the phosphor at a second wavelength are then additively emitted fromthe phosphor-converted LED device. It is appreciated by those skilled inthe art that the LED may be designed to emit blue photons, and thephosphor may be designed to emit yellow photons, in ratios where theadditive output is perceived by the human eye as white light.

In an example of fabricating a phosphor-converted LED device, thephosphor is dispersed in a suitable encapsulant in a liquid phase andthen deposited onto the LED. The phosphor generally migrates downward inthe encapsulant following deposition, as the encapsulant cures to asolid form. This migration often leads to uneven layering of thephosphor over the LED, which results in a phosphor-converted LED deviceproducing a wide white color bin spread. As an example of problemsassociated with this conventional fabrication method, if the shape ofthe LED is a rectangular prism, then the phosphor may sink to the bottomof the phosphor-encapsulant dispersion to the point that furthermigration of the phosphor is partially impeded by the LED itself. Asthis impedance develops while the phosphor dispersion cures, thephosphor may become unevenly distributed across the upper surface of theLED rectangular prism onto which it sinks. In particular, portions ofthe sinking phosphor that clear the outer edges of the top surface ofthe LED may further sink below that surface. As a result, the thicknessof the phosphor layer may be decreased near the outer edges. Uponstimulation of electroluminescent emissions from the LED itself, thisdecreased thickness may result in reduced capacity by the phosphor nearthe outer edges to convert the photons emitted by the LED by stimulatedemissions. This reduced capacity imbalances the desired ratio betweenblue and yellow photons emitted from the phosphor-converted LED devicein regions over the outer edges, because the yellow photonic emissionsthere are reduced. Hence, a wide white color bin spread may result and ablue halo may be generated in the photonic output of thephosphor-converted LED device, roughly conforming to the locations ofthe thin regions in the phosphor near such outer edges. This blue haloconstitutes a non-uniformity in the light output from thephosphor-converted LED device that may be both aesthetically andfunctionally undesirable in use of the device.

Therefore, as phosphor-converted LED devices are implemented for diverseend use applications, there is a continuing need to provide newphosphor-converted LED device structures generating photonic emissionsof improved uniformity.

SUMMARY

A New Phosphor-Converted LED Device (“NPCLD”) is described. The NPCLDmay include a concave base housing, light emitting diode (“LED”) in theconcave base housing, phosphor body over the LED, and a first lens overthe phosphor body. The LED may include a p-doped semiconductor body andan n-doped semiconductor body, and the phosphor body may have asubstantially convex upper surface, and the first lens may have asubstantially convex upper surface.

Alternatively, the NPCLD may include a concave base housing, LED in theconcave base housing, phosphor body over the LED, first lens over theLED, and second lens over the phosphor body and over the first lens. TheLED may include a p-doped semiconductor body and an n-dopedsemiconductor body, and the phosphor body may have a substantially flatupper surface. Additionally, the first lens may have a substantiallyflat upper surface, and the second lens may include a substantiallyconvex upper surface. Moreover, the first lens and the phosphor bodytogether may have a substantially flat interface.

As an example, the NPCLD may be fabricated by producing a concave basehousing and placing the LED in the concave base housing where the LEDmay include a p-doped semiconductor body and an n-doped semiconductorbody. A phosphor body may be formed over the LED and a first lens may beformed over the LED, where the first lens may have a substantially flatupper surface. Additionally, a second lens may be formed over thephosphor body and over the first lens, where the second lens may have asubstantially convex upper surface, and the first lens and the phosphorbody may be shaped to have a substantially flat interface.

In an additional implementation example, a method for fabricating theNPCLD may include forming a phosphor body having a substantially convexupper surface over an LED, and forming a lens over the phosphor bodyhaving a substantially convex upper surface.

Other systems, methods and features of the invention will be or willbecome apparent to one with skill in the art upon examination of thefollowing figures and detailed description. It is intended that all suchadditional systems, methods, features and advantages be included withinthis description, be within the scope of the invention, and be protectedby the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 shows a cross-sectional view of an example of an implementationof a new phosphor-converted LED device (“NPCLD”);

FIG. 2 shows a flowchart illustrating an example of an implementation ofa method for fabricating the NPCLD shown in FIG. 1;

FIG. 3 shows a cross-sectional view of an example of anotherimplementation of the NPCLD;

FIG. 4 shows a flowchart illustrating an example of an implementation ofa method for fabricating the NPCLD shown in FIG. 3;

FIG. 5 shows a cross-sectional view of an example of yet anotherimplementation of the NPCLD;

FIG. 6 shows a flowchart illustrating an example of an implementation ofa method for fabricating the NPCLD shown in FIG. 5.

FIG. 7 shows a cross-sectional view of an example of yet anotherimplementation of the NPCLD; and

FIG. 8 shows a flowchart illustrating an example of an implementation ofa method for fabricating the NPCLD shown in FIG. 7.

DETAILED DESCRIPTION

In the following description of various implementations, reference ismade to the accompanying drawings that form a part of this disclosure,and which show, by way of illustration, specific implementations inwhich the invention may be practiced. Other implementations may beutilized and structural changes may be made without departing from thescope of the present invention.

In FIG. 1, a cross-sectional view of an example of an implementation ofa new phosphor-converted LED device (“NPCLD”) 100 is shown in accordancewith the invention. The NPCLD 100 includes an anode 102 and a cathode104. The cathode 104 includes a concave (i.e., bowl and/or cup-shaped)base housing 106 formed of an electrical insulator and supported on aframe 107, in which an LED 108 is placed. The frame 107 may beintegrated with the cathode 104, and may be fabricated, for example,from lead. It will be understood by those skilled in the art that theframe 107 may alternatively be any form of printed circuit board, suchas, for example, one fabricated of FR4, FR5, bismaleimide/triazine (BT),polyimide, metal core. It is also understood that the frame 107 mayinstead be in another form, such as for example a metal coated ceramicframe, a plastic substrate, or a lead frame with a plastic body orcavity. The LED 108 may include a p-doped semiconductor body 110 and ann-doped semiconductor body 112. It is appreciated by those skilled inthe art that the term “body” broadly means and includes all forms of amass of a subject device element, such as, for example, a layer,multiple layers, a coating, a casting, or a block, of any suitabledimensions, however formed. In an example of an implementation, theshape of the LED 108 may be a rectangular prism. In other examples, theshape of the LED 108 may be cubic, cylindrical, or have anotherdesirable geometric shape. In an example of an implementation, more thanone LED 108 may be placed in the concave base housing 106.

The p-doped semiconductor body 110 may be in signal communication with abase conductor 114 and the n-doped semiconductor body 112 may be insignal communication with a top conductor 116. The base conductor 114and top conductor 116 allow current to flow in and out of the p-dopedsemiconductor body 110 and n-doped semiconductor body 112, respectively.A cathode bonding wire 118 may electrically connect the cathode 104 tothe base conductor 114 placing the cathode 104 in signal communicationwith the base conductor 114. Similarly, an anode bonding wire 120 mayelectrically connect the anode 102 to the top conductor 116. In anexample of an implementation, more than one cathode bonding wire 118and/or more than one anode bonding wire 120 may be used. In analternative implementation example, the concave base housing 106 may beformed of an electrical conductor, and the base conductor 114 and thecathode bonding wire 118 may be omitted. It will be appreciated that inan alternative example structure for the NPCLD, the semiconductor body112 may be p-doped and the semiconductor body 110 may be n-doped. Acurrent flow through the LED 108 in such an alternative structure may bereversed, so that the NPCLD 100 may include an anode 104 and a cathode102. In another implementation example, the cathode 104 may be replacedby a first terminal 104 at a relatively high electrical potential insignal communication with the p-doped semiconductor body 110; and theanode 102 may be replaced by a second terminal 102 at a relatively lowelectrical potential in signal communication with the n-dopedsemiconductor body 112. The LED 108 may be substantially covered by aphosphor body 122 formed from a composition including a phosphor and aphosphor encapsulant. By “substantially” is meant that only a minorportion or none of the surface of the covered element of the NPCLD isexposed through the covering material. The phosphor body 122 may have aphosphor domed surface 124 forming a substantially convex lens forexample photonic emissions 126, 128, 130 and 132 from the phosphor body122. It is appreciated that the phrase “substantially convex” means thatthe phosphor body 122 has a generally convex shape, which may includeminor imperfections. The inner walls (such as side inner wall 134 andbase inner wall 136) of the concave base housing 106 form a reflectorfor the photons emitted by both the LED 108 and the phosphor body 122.The reflector generally deflects these photons in a direction 140 ofmaximum photonic radiation from the NPCLD 100. As an example, the baseinner wall 136 may have a circular circumference and the concave basehousing 106 may also have a circular circumference. It is appreciated,however, that the base inner wall 136 and the concave base housing 106may also have circumferences of other shapes. For example, the baseinner wall 136 may have a circumference that is elliptical,quadrilateral, or of some other geometric shape. Desirably, thecircumference of the base inner wall 136 has at least one axis ofsymmetry, and desirably the shape of the circumference of the concavebase housing 106 is similar to that of the base inner wall 136. Theanode 102 and cathode 104 of the NPCLD 100 may be supported on a base142, and collectively encapsulated in a diffused lens 144 having anencapsulation domed surface 146 forming a substantially convex lens forexample photonic emissions 148, 150, 152 and 154 from the NPCLD 100.

In an example of operation, a bias current is applied across the anode102 and cathode 104 by an external power source, not shown. The biascurrent induces charge carriers to be transported across the interface156 between the n-doped semiconductor body 112 and the p-dopedsemiconductor body 110. Electrons flow from the n-doped semiconductorbody 112 to the p-doped semiconductor body 110, and holes are generatedin the opposite direction. Electrons injected into the p-dopedsemiconductor body 110 recombine with the holes, resulting inelectroluminescent emission of photons such as example photons 158 and160 from the LED 108. Some of these photons pass through the phosphorbody 122 and are emitted through the encapsulation domed surface 146.Other photons stimulate luminescent emission of new photons such asexample photons 126, 128, 130 and 132 by the phosphor in the phosphorbody 122. The combination of the phosphor domed surface 124, forming asubstantially convex lens, and the encapsulation domed surface 146,forming a substantially convex lens, function together to accentuateuniformity of the spectral distribution and intensity of photons emittedfrom the encapsulation domed surface 146 of the NPCLD 100.

In an example of an implementation, sufficient phosphor may be utilizedin the composition to form the phosphor body 122 so that phosphorsubstantially covers the LED 108. Furthermore, the phosphor may beselected to have a relatively higher density (or specific gravity) thanthe encapsulant in which it is dispersed, so that the phosphor sinks tothe bottom of the phosphor body 122. As indicated by the dotted line162, in this implementation example the phosphor forms a dome shapedportion 164 of the phosphor body 122. Formation of the phosphor into thedome shaped portion 164 of the phosphor body 122 further accentuatesuniformity of electroluminescent photonic emissions from the phosphorbody 122.

The substantially convex phosphor domed surface 124 of the phosphor body122 accentuates the output of photons into the diffused lens 144. It isappreciated that according to Snell's Law, light travels from a mediumof higher refractive index into a medium of lower refractive index onlyif it intersects the interface between the two media at an angle lessthan the critical angle for the two media. The curvature of thesubstantially convex phosphor domed surface 124 causes most photonsleaving the phosphor body 122 to meet the substantially convex phosphordomed surface 124 at nearly right angles, so that the photons enter thediffused lens 144 with little reflection loss.

The choice of materials for fabricating the LED 108 is generallydetermined by the desired end use application for the NPCLD 100. Forexample, if photonic emissions interpreted by the human eye as whitelight are desired, the LED may be designed to emit blue light. Galliumnitride- (“GaN-”) or indium-gallium-nitride (“InGaN-”) based LEDsemiconductor chips emitting blue light with an emission maximum broadlywithin a range of about 420 nanometers (“nm”) to about 490 nm, or moreparticularly within a range of about 430 nm to about 480 nm, may beutilized. The term “GaN- or InGaN-based LED” is to be understood asbeing an LED whose radiation-emitting region contains GaN, InGaN and/orrelated nitrides, together with mixed crystals based on such nitrides,such as Ga(Al—In)N, for example. Such LEDs are known, for example, fromShuji Nakamura and Gerhard Fasol, “The Blue Laser Diode”, SpringerVerlag, Berlin/Heidelberg, 1997, pp. 209 et seq., the entirety of whichhereby is incorporated herein by reference. In an alternativeimplementation example, a polymer LED or laser diode may be utilizedinstead of the semiconductor LED. It is appreciated that the term “lightemitting diode” is defined as encompassing and including semiconductorlight emitting diodes, polymer light emitting diodes, and laser diodes.

Similarly, the choice of phosphors for excitation by some of the bluephotons emitted by the LED also may be determined by the desired end useapplication for the NPCLD 100. As an example, if photonic emissionsinterpreted by the human eye as white light are desired, the selectedphosphor may be designed to emit yellow light. When combined inappropriate ratios at appropriate wavelengths as shown, for example, inchromaticity charts published by the International Commission forIllumination, the blue and yellow photons appear together as whitelight. In this regard, yttrium aluminum garnet (“YAG”) is a common hostmaterial, and is usually doped with one or more rare-earth elements orcompounds. Cerium is a common rare-earth dopant in YAG phosphorsutilized for white light emission applications.

In an example of an implementation, the selected phosphor may be acerium-doped yttrium-aluminum garnet including at least one element suchas yttrium, lutetium, selenium, lanthanum, gadolinium, samarium, orterbium. The cerium-doped yttrium-aluminum garnet may also include atleast one element such as aluminum, gallium, or indium. In an example ofanother implementation, the selected phosphor may have a cerium-dopedgarnet structure A3B5O12, where the first component “A” represents atleast one element such as yttrium (“Y”), lutetium (“Lu”), selenium(“Se”), lanthanum (“La”), gadolinium (“Gd”), samarium (“Sm”), or terbium(“Tb”) and the second component “B” represents at least one element suchas aluminum (Al), gallium (Ga), or indium (In). These phosphors may beexcited by blue light from the LED 108 and in turn may emit light whosewavelength is shifted into the range above 500 nm, ranging up to about585 nm. As an example, a phosphor may be utilized having a wavelength ofmaximum emission that is within a range of about 550 nm to about 585 nm.In the case of cerium-activated Tb-garnet luminescent materials, theemission maximum may be at about 550 nm. Relatively small amounts of Tbin the host lattice may serve the purpose of improving the properties ofcerium-activated luminescent materials, while larger amounts of Tb maybe added specifically to shift the emission wavelength ofcerium-activated luminescent materials. A high proportion of Tb istherefore well suited for white phosphor-converted LED devices with alow color temperature of less than 5000 K. For further backgroundinformation on phosphors for use in phosphor-converted LED devices, seefor example: WO 98/05078; WO 97/50132; WO 98/12757; and WO 97/50132,which are herein incorporated by reference in their entirety.

As an example, a blue-emitting LED based on gallium nitride orindium-gallium nitride, with emission maxima within a range of about 430nm to about 480 nm, may be utilized to excite a luminescent material ofthe YAG:Ce type with emission maxima within a range of about 560 nm toabout 585 nm.

Disclosed are various examples of implementations where a NPCLD isdesigned to combine blue photons generated by LED 108electroluminescence and yellow photons generated from bluephoton-stimulated phosphor 122 luminescence, in order to provide lightoutput having a white appearance. However, it is appreciated that NPCLDsoperating with different chromatic schemes may also be designed forproducing light that appears to be white or appears to have anothercolor. Light that appears to be white may be realized through manycombinations of two or more colors generated by LED 108electroluminescence and photon-stimulated phosphor 122 luminescence. Oneexample method for generation of light having a white appearance is tocombine light of two complementary colors in the proper power ratio.With regard to the LED 108 itself, photon-emitting diode p-n junctionsare typically based on two selected mixtures of Group III and Group Velements, such as gallium arsenide, gallium arsenide phosphide, orgallium phosphide. Careful control of the relative proportions of thesecompounds, and others incorporating aluminum and indium, as well as theaddition of dopants such as tellurium and magnesium, enables productionof LEDs that emit, for example, red, orange, yellow, or green light. Asan example, the following semiconductor compositions may be utilized togenerate photons in the indicated spectral ranges:gallium-aluminum-arsenide/gallium arsenide (epitaxial layers/LEDsubstrate; output wavelength 880 nm, infrared);gallium-aluminum-arsenide/gallium-aluminum-arsenide (660 nm, ultra red);aluminum-gallium-indium-phosphide (epitaxial layers; output wavelength633 nm, super red); aluminum-gallium-indium-phosphide (612 nm, superorange); gallium-arsenide/gallium-phosphide (605 nm, orange);gallium-arsenide-phosphide/gallium-phosphide (585 nm, yellow);indium-gallium-nitride/silicon-carbide (color temperature 4500K,incandescent white); indium-gallium-nitride/silicon-carbide 6500K, palewhite); indium-gallium-nitride/silicon-carbide (8000K, cool white);gallium-phosphide/gallium-phosphide (555 nm, pure green);gallium-nitride/silicon-carbide (470 nm, super blue);gallium-nitride/silicon-carbide (430 nm, blue violet); andindium-gallium-nitride/silicon-carbide (395 nm, ultraviolet).

As an example, a phosphor selected as discussed above may be dispersedin an encapsulant, forming a phosphor-encapsulant composition fordeposition onto the LED 108 in the fabrication of the NPCLD 100. Theencapsulant is at least partially transparent to the generated photonicradiation. As an example of an implementation, the encapsulant may be acurable polymeric resin, such as an epoxy, silicone or acrylate resin(such as polymethyl-methacrylate for example), or a mixture of suchresins. In an example of another implementation, the encapsulant may beanother photonic radiation-transmissive material, such as an inorganicglass that may be in the form of a sol-gel, for example.

In FIG. 2, a flowchart 200 is shown illustrating an example of animplementation of a process for fabricating the new NPCLD 100 shown inFIG. 1. The process begins in step 202, and in step 204, a cathode 104having a concave base housing 106 is produced, wherein the concave basehousing 106 has photon-reflective side inner wall 134 and base innerwall 136. An LED 108 is placed within the concave base housing 106 onthe base inner wall 136, in step 206. The LED may be pre-made, or formedin situ. The LED 108 may be positioned at a point on the base inner wall136 substantially equidistant from all points at which base inner wall136 meets side inner wall 134. The LED 108 may be fabricated usingvarious known techniques such as, for example, liquid phase epitaxy,vapor phase epitaxy, metal-organic epitaxial chemical vapor deposition,or molecular beam epitaxy. In step 208, the cathode 104 and anode 102are positioned on a base 142, and bonding wires 118 and 120 areconnected to the conductors 114 and 116 and to the cathode 104 and anode102, respectively. It is appreciated that either all or a portion ofstep 208 may be performed later in the process without departing fromthe method. A phosphor-encapsulant composition is then formulated asdiscussed above. As an example, the concentration of phosphor in thephosphor-encapsulant composition may be sufficiently high so that uponformation of the phosphor body 122, sufficient phosphor is depositedwithin the concave base housing 106 to substantially cover the LED 108as shown by the dotted line 162, FIG. 1. In this example, the presenceof the LED 108 onto which the phosphor sinks further contributes to theoccupation by the phosphor of a sub-body within the phosphor body 122having a substantially convex surface defined by the dotted line 162. Instep 210, a phosphor body 122 is formed within the concave base housing106 on the LED 108. In this example of an implementation, the phosphorbody 122 is formed to have a substantially convex phosphor domed surface124. As an example, the phosphor body 122 may be molded or cast into thedesired shape. In step 212, the LED 108, anode 102, cathode 104, andbonding wires 118 and 120 of the NPCLD 100 are embedded in a diffusedlens 144. The process then ends in step 214. The diffused lens may befabricated from an encapsulant as discussed earlier, having dispersedlight-scattering particles such as titanium dioxide or silicon dioxideparticles. Additionally, the diffused lens 144 may be formed with thedesired dome shape, for example, by molding or casting.

In FIG. 3, a cross-sectional view of an example of anotherimplementation of a new NPCLD 300 is shown. The NPCLD 300 includes ananode 302, and a cathode 304. Similar to FIG. 2, the cathode 304includes a concave base housing 306 formed of an electrical insulatorand supported on a frame 307, in which an LED 308 is placed. The frame307 may be integrated with the cathode 304, and may be fabricated, forexample, from lead or another material as earlier discussed. The LED 308includes a p-doped semiconductor body 310 and an n-doped semiconductorbody 312. In an example of an implementation, more than one LED 308 maybe placed in the concave base housing 306.

The p-doped semiconductor body 310 may be in signal communication with abase conductor 314 and the n-doped semiconductor body 312 may be insignal communication with a top conductor 316. A cathode bonding wire318 may electrically connect the cathode 304 to the base conductor 314placing the cathode 304 in signal communication with the base conductor314. An anode bonding wire 320 may electrically connect the anode 302with the top conductor 316 placing the anode 302 in signal communicationwith the top conductor 316 In an example of an implementation, more thanone cathode bonding wire 318 and/or more than one anode bonding wire 320may be used. Similar to FIG. 1, the base conductor 314 and top conductor316 allow current to flow in and out of the p-doped semiconductor body310 and n-doped semiconductor body 312, respectively. In an alternativeimplementation example, the concave base housing 306 may be formed of anelectrical conductor, and the base conductor 314 and the cathode bondingwire 318 may be omitted. It will be appreciated that in an alternativeexample structure for the NPCLD, the semiconductor body 312 may bep-doped and the semiconductor body 310 may be n-doped. A current flowthrough the LED 308 in such an alternative structure may be reversed, sothat the NPCLD 300 may include an anode 304 and a cathode 302. Inanother implementation example, the cathode 304 is replaced by a firstterminal 304 at a relatively high electrical potential in signalcommunication with the p-doped semiconductor body 310; and the anode 302is replaced by a second terminal 302 at a relatively low electricalpotential in signal communication with the n-doped semiconductor body312.

The LED 308 may be substantially covered by a first diffused lens body322 formed from a composition including diffusant particles and anencapsulant. The diffusant particles may be, for example, particles of ametal oxide such as titanium dioxide or silicon dioxide. The firstdiffused lens body 322 has a substantially flat upper surface 324. It isappreciated that the phrase “substantially flat” means that the uppersurface 324 of the first diffused lens body 322 has a generally flatshape, which may include minor imperfections. A phosphor body 326 isdeposited on the substantially flat upper surface 324, having a firstsubstantially convex upper surface 328. The substantially flat uppersurface 324 on which the phosphor body 326 is deposited, allows thephosphor to sink evenly through the encapsulant. In this manner,differential concentrations of phosphor across the substantially flatupper surface 324 are minimized. In addition, deposition of the phosphorbody 326 onto the substantially flat upper surface 324 permits precisecontrol over the effective thickness in the direction 330 of thephosphor within the phosphor body 326. This precise thickness controlenables precise adjustment of the spectral ratio of photons emitted bythe NPCLD 300, in turn enabling control over the appearance of the colorof the photonic output to the human eye. Furthermore, the first convexupper surface (i.e., the domed surface) 328 of the phosphor body 326facilitates generation of substantially uniform intensities of photonspassing through the first domed surface 328. The side inner wall 332 andbase inner wall 334 of the concave base housing 306 form a reflector forthe photons emitted by the LED 308 and by the phosphor body 326, anddeflect these photons in the direction 330 of maximum photonic radiationof the NPCLD 300. The side inner wall 332 may have a circularcircumference. The anode 302 and cathode 304 of the NPCLD 300 may besupported on a base 336, and collectively encapsulated in a second lens338 that may be a diffused lens, having a second domed surface 340forming a substantially convex lens for example photonic emissions 342,344, 346 and 348 from the NPCLD 300. In an implementation example, thesecond lens 338 may not be a diffused lens.

FIG. 4 shows flowchart 400 illustrating an example of an implementationof a method for fabricating the new NPCLD 300 shown in FIG. 3. Theprocess begins at step 402 and in step 404, a cathode 304 having aconcave base housing 306 is produced. The concave base housing 306 has aphoton-reflective side inner wall 332 and a base inner wall 334, shownin FIG. 3. In step 406, an LED 308 is placed within the concave basehousing 306 on the base inner wall 334. In one implementation of amethod, the LED 308 may be placed at a point on the base inner wall 334substantially equidistant from all points at which side inner wall 332meets base inner wall 334. In step 408, the cathode 304 and anode 302are positioned on a base 336, and bonding wires 318 and 320 areconnected from the base conductor 314 to the cathode 304 and from thetop conductor 316 to the anode 302, respectively. Again, it isappreciated that all or a portion of step 408 may be performed later inthe process. In step 410, a first diffused lens body 322 is placedwithin the concave base housing 306, substantially covering the LED 308and forming the substantially flat upper surface 324. The first diffusedlens body 322 may be formed from the same composition as discussed abovein connection with step 212 of FIG. 2. A phosphor-encapsulantcomposition is formulated as earlier discussed. In step 412, thephosphor body 326 is formed on the substantially flat upper surface 324,having a first substantially convex upper surface 328. As an example,the phosphor body 326 may be molded or cast into any desired shape. Instep 414, the LED 308, anode 302, cathode 304, and bonding wires 318 and320 of the NPCLD 300 are embedded in the second lens 338. The processthen ends in step 416. As an example of an implementation, the secondlens 338 is fabricated from an encapsulant as earlier discussed, havingdispersed light-scattering particles such as titanium dioxide or silicondioxide particles. The second lens 338 may be formed with the desireddome shape, for example, by molding or casting.

In FIG. 5, a cross-sectional view of an example of anotherimplementation of a new NPCLD 500 is shown. The NPCLD 500 includes ananode 502, and a cathode 504. The cathode 504 includes a concave basehousing 506 formed of an electrical insulator and supported on a frame507, in which an LED 508 is placed. The frame 507 may be integrated withthe cathode 504, and may be fabricated, for example, from lead oranother material as earlier discussed. The LED 508 includes a p-dopedsemiconductor body 510 and an n-doped semiconductor body 512. In anexample of an implementation, more than one LED 508 may be placed in theconcave base housing.

The p-doped semiconductor body 510 may be in signal communication with abase conductor 514 and the n-doped semiconductor body 512 may be insignal communication with a top conductor 516. The base conductor 514and top conductor 516 allow current to flow in and out of the p-dopedsemiconductor body 510 and n-doped semiconductor body 512, respectively.A cathode bonding wire 518 may electrically connect the cathode 504 tothe base conductor 514 placing the cathode 504 in signal communicationwith the base conductor 514. Similarly, an anode bonding wire 520 mayelectrically connect the anode 502 to the top conductor 516. In analternative implementation example, the concave base housing 506 may beformed of an electrical conductor, and the base conductor 514 and thecathode bonding wire 518 may be omitted. In an example of animplementation, more than one cathode bonding wire 518 and/or more thanone anode bonding wire 520 may be used. It will be appreciated that inan alternative example structure for the NPCLD, the semiconductor body512 may be p-doped and the semiconductor body 510 may be n-doped. Acurrent flow through the LED 508 in such an alternative structure may bereversed, so that the NPCLD 500 may include an anode 504 and a cathode502. In another implementation example, the cathode 504 is replaced by afirst terminal 504 at a relatively high electrical potential in signalcommunication with the p-doped semiconductor body 510; and the anode 502is replaced by a second terminal 502 at a relatively low electricalpotential in signal communication with the n-doped semiconductor body512.

The LED 508 may be substantially covered by a phosphor body 522 formedfrom a composition including a phosphor and an encapsulant. The phosphorbody 522 has a substantially flat upper surface 524. A first diffusedlens 526 having a substantially flat upper surface 528 is placed on thephosphor body 522. The first diffused lens 526 disperses photons acrossthe surface 528, reducing imbalances in photonic intensity and photonicspectral ratios. The side inner wall 530 and base inner wall 532 of theconcave base housing 506 form a reflector for the photons emitted by theLED 508 and by the phosphor body 522, and deflect these photons in thedirection 534 of maximum photonic radiation of the NPCLD 500. The baseinner wall 532 may have a circular circumference. The anode 502 andcathode 504 of the NPCLD 500 may be supported on a base 535, andcollectively encapsulated in a second lens 536, which may be a diffusedlens, having a domed surface 538 forming a substantially convex lens forexample photonic emissions 540, 542, 544, and 546 from the NPCLD 500. Inan implementation example, the second lens 536 may not be a diffusedlens.

In an example of an implementation, the phosphor in the compositionutilized to form the phosphor body 522 is of sufficient concentrationand amount to substantially cover the LED 508. Furthermore in thisexample, the phosphor may be selected to have a relatively higherdensity than the encapsulant in which it is dispersed, so that thephosphor sinks to the bottom of the phosphor body 522. In this example,the phosphor covers the LED 508 by a minimum distance “x,” shown by thearrow 548, which is sufficiently great such that the phosphor forms asub-body within the phosphor body 522, having a substantially flat uppersurface indicated by the dotted line 550. This substantially flat uppersurface reduces irregularities in the intensity and spectral ratios ofphotons reaching the substantially flat upper surface 524.

In FIG. 6, a flowchart 600 illustrating an example of an implementationof a method for fabricating the new NPCLD 500 of FIG. 5 is shown. Theprocess begins in step 602, and in step 604, a cathode 504 having theconcave base housing 506 is produced, wherein the concave base housing506 has photon-reflective side inner wall 530 and base inner wall 532.An LED 508 is placed within the concave base housing 506 on the baseinner wall 532, in step 606. The LED 508 may be positioned at a point onthe base inner wall 532 substantially equidistant from all points atwhich base inner wall 532 meets side inner wall 530. In step 608, thecathode 504 and anode 502 are positioned on a base 535, and bondingwires 518 and 520 are connected to the conductors 514 and 516 and to thecathode 504 and anode 502, respectively. Again, it is appreciated thateither all or a portion of step 608 may be performed later in theprocess 600 without departing from the method. A phosphor-encapsulantcomposition is formulated as earlier discussed in FIGS. 2 and 4. In step610, a phosphor body 522 is formed within the concave base housing 506on the LED 508. In this example, the phosphor body 522 is formed to havethe substantially flat upper surface 524 shown in FIG. 5. In an exampleof an implementation, the concentration and amount of phosphor in thephosphor-encapsulant composition is sufficiently high so that uponformation of the phosphor body 522, sufficient phosphor is depositedwithin the concave base housing 506 to substantially cover the LED 508as shown by the dotted line 550. In step 612, a first diffused lens 526is formed on the phosphor body 522, having a substantially flat uppersurface 528. In an implementation example, the first diffused lens 526may be fabricated from an encapsulant as earlier discussed, havingdispersed light-scattering particles such as titanium dioxide or silicondioxide particles. The first diffused lens 526 may be formed, forexample, by dispensing a curable composition including light scatteringparticles dispersed in an encapsulant. Alternatively, the first diffusedlens 526 may be screen-printed, or pre-formed as a solid film andattached onto the phosphor body 522. In step 614, the LED 508, anode502, cathode 504, and bonding wires 518 and 520 of the NPCLD 500 areembedded in the second lens 536. The second lens 536 may be formed witha dome shape, for example, by molding or casting. The process then endsin step 616.

In FIG. 7, a cross-sectional view of an example of yet anotherimplementation of a new NPCLD 700 is shown. The NPCLD 700 includes ananode 702, and a cathode 704. The cathode 704 includes a concave basehousing 706 formed of an electrical insulator and supported on a frame707, in which an LED 708 is placed. The frame 707 may be integrated withthe cathode 704 and may be fabricated, for example, from lead or anothermaterial as earlier discussed. The LED 708 includes a p-dopedsemiconductor body 710 and an n-doped semiconductor body 712. In anexample of an implementation, more than one LED 708 may be placed in theconcave base housing 706.

The p-doped semiconductor body 710 may be in signal communication with abase conductor 714 and the n-doped semiconductor body 712 may be insignal communication with a top conductor 716. The base conductor 714and top conductor 716 allow current to flow in and out of the p-dopedsemiconductor body 710 and n-doped semiconductor body 712, respectively.A cathode bonding wire 718 may electrically connect the cathode 704 tothe base conductor 714 placing the cathode 704 in signal communicationwith the base conductor 714. Similarly, an anode bonding wire 720 mayelectrically connect the anode 702 to the top conductor 716. In analternative implementation example, the concave base housing 706 may beformed of an electrical conductor, and the base conductor 714 and thecathode bonding wire 718 may be omitted. In an example of animplementation, more than one cathode bonding wire 718 and/or more thanone anode bonding wire 720 may be used. It will be appreciated that inan alternative example structure for the NPCLD, the semiconductor body712 may be p-doped and the semiconductor body 710 may be n-doped. Acurrent flow through the LED 708 in such an alternative structure may bereversed, so that the NPCLD 700 may include an anode 704 and a cathode702. In another implementation example, the cathode 704 is replaced by afirst terminal 704 at a relatively high electrical potential in signalcommunication with the p-doped semiconductor body 710; and the anode 702is replaced by a second terminal 702 at a relatively low electricalpotential in signal communication with the n-doped semiconductor body712.

The LED 708 is substantially covered by a first diffused lens 722 havinga substantially flat upper surface 724. A phosphor body 726 formed froma composition including a phosphor and an encapsulant is deposited onthe first diffused lens 722. The phosphor body 726 has a substantiallyflat upper surface 728. The first diffused lens 722 disperses photonsacross the surface 728, reducing imbalances in photonic intensity andphotonic spectral ratios. The substantially flat upper surface 724 onwhich the phosphor body 726 is formed, ensures that as the phosphorsinks through the encapsulant, it does so evenly across thesubstantially flat upper surface 724. In this manner, differentialconcentrations of phosphor across the substantially flat upper surface724 are minimized. In addition, deposition of the phosphor body 726 ontothe substantially flat upper surface 724 permits precise control overthe effective thickness in the direction 730 of the phosphor within thephosphor body 726. This precise thickness control enables preciseadjustment of the spectral ratio of photons emitted by the NPCLD 700, inturn enabling control over appearance of the color of the photonicoutput to the human eye. The side inner wall 732 and base inner wall 734of the concave base housing 706 form a reflector for the photons emittedby the LED 708 and by the phosphor body 722, and deflect these photonsin the direction 730 of maximum photonic radiation of the NPCLD 700. Thebase inner wall 734 may have a circular circumference. The anode 702 andcathode 704 of the NPCLD 700 may be supported on a base 736, andcollectively encapsulated in a second lens 738, which may be a diffusedlens, having a domed surface 740 forming a substantially convex lens forexample photonic emissions 742, 744, 746, and 748 from the NPCLD 700. Inan implementation example, the second lens 738 may not be a diffusedlens.

In FIG. 8, a flowchart 800 is shown that illustrates an example of animplementation of a method for fabricating the new NPCLD 700 of FIG. 7.The process begins in step 802, and in step 804, a cathode 704 having aconcave base housing 706 is produced, wherein the concave base housing706 has photon-reflective side inner wall 732 and base inner wall 734.An LED 708 is placed within the concave base housing 706 on the baseinner wall 734, in step 806. The LED 708 may be positioned at a point onthe base inner wall 734 substantially equidistant from all points atwhich base inner wall 734 meets side inner wall 732. In step 808, thecathode 704 and anode 702 are positioned on a base 736, and bondingwires 718 and 720 are connected to the conductors 714 and 716 and to thecathode 704 and anode 702, respectively. Again, it is appreciated thateither all or a portion of step 808 may be performed later in theprocess without departing from the method. In step 810, a first diffusedlens 722 is formed within the concave base housing 706 on the LED 708,having a substantially flat upper surface 724. As an example, thediffused lens 722 may be fabricated from an encapsulant as earlierdiscussed, having dispersed light-scattering particles such as titaniumdioxide or silicon dioxide particles. Similar to the processes describedin FIGS. 2, 4, and 6, a phosphor-encapsulant composition is formulatedas earlier discussed. In step 812, the phosphor body 726 is formedwithin the concave base housing 706 on the substantially flat uppersurface 724. In this example, the phosphor body 726 may be formed tohave a substantially flat upper surface 728. In an example of animplementation, the phosphor body 726 may be fabricated from anencapsulant as earlier discussed, having dispersed phosphor. Thephosphor body 726 may be formed, for example, by dispensing a curablecomposition including the phosphor dispersed in an encapsulant.Alternatively, the phosphor body 726 may be screen-printed, orpre-formed as a solid film and attached onto the diffused lens 722. Instep 814, the LED 708, anode 702, cathode 704, and bonding wires 718 and720 of the NPCLD 700 are embedded in a second lens 738. The second lens738 may be formed with the desired dome shape, for example, by moldingor casting. The process then ends in step 816.

While the foregoing description refers to the use of an LED emittingblue photons to stimulate luminescent emissions from a yellow phosphorin order to produce output light having a white appearance, the subjectmatter is not limited to such a device. Any phosphor-converted LEDdevice that could benefit from the functionality provided by thecomponents described above may be implemented in the NPCLDs disclosedherein and shown in the drawings.

Moreover, it will be understood that the foregoing description ofnumerous implementations has been presented for purposes of illustrationand description. This description is not exhaustive and does not limitthe claimed inventions to the precise forms disclosed. Modifications andvariations are possible in light of the above description or may beacquired from practicing the invention. The claims and their equivalentsdefine the scope of the invention.

1. A New Phosphor-Converted LED Device (“NPCLD”), comprising: a concavebase housing; a light emitting diode (“LED”) in the concave basehousing, the LED having a p-doped semiconductor body and an n-dopedsemiconductor body; a phosphor body over the LED, the phosphor bodyhaving a substantially flat upper surface; a first lens over the LED,the first lens having a substantially flat upper surface; and a secondlens over the phosphor body and over the first lens, the second lenshaving a substantially convex upper surface; and the first lens and thephosphor body together having a substantially flat interface.
 2. TheNPCLD of claim 1, wherein the phosphor body is interposed between theLED and the first lens.
 3. The NPCLD of claim 1, wherein the phosphorbody includes a phosphor and an encapsulant, wherein the phosphorsubstantially covers the LED.
 4. The NPCLD of claim 1, wherein the firstlens is interposed between the LED and the phosphor body.
 5. The NPCLDof claim 1, wherein: the LED has an emission maximum within a range ofabout 420 nanometers to about 490 nanometers, the n-doped semiconductorbody and the p-doped semiconductor body each including a member selectedfrom the group consisting of gallium nitride, indium-gallium-nitride,gallium-aluminum-indium-nitride, and mixtures; and the phosphor has anemission maximum within a range of about 550 nanometers to about 585nanometers, the phosphor including a cerium-doped yttrium-aluminumgarnet, including at least one element selected from the groupconsisting of yttrium, lutetium, selenium, lanthanum, gadolinium,samarium, and terbium; and at least one element selected from the groupconsisting of aluminum, gallium, and indium.
 6. The NPCLD of claim 1,further including: a first terminal at a relatively high electricalpotential in signal communication with the p-doped semiconductor body;and a second terminal at a relatively low electrical potential in signalcommunication with the n-doped semiconductor body.
 7. A method forfabricating a New Phosphor-Converted LED Device (“NPCLD”), the methodcomprising: producing a concave base housing; placing a light emittingdiode (“LED”) in the concave base housing, the LED having a p-dopedsemiconductor body and an n-doped semiconductor body; forming a phosphorbody over the LED; forming a first lens over the LED, the first lenshaving a substantially flat upper surface; and forming a second lensover the phosphor body and over the first lens, the second lens having asubstantially convex upper surface; and shaping the first lens and thephosphor body to have a substantially flat interface.
 8. The method ofclaim 7, further including interposing the phosphor body between the LEDand the first lens.
 9. The method of claim 7, further includingsubstantially covering the LED with phosphor.
 10. The method of claim 7,further including interposing the first lens between the LED and thephosphor body.
 11. The method of claim 10, further including shaping thephosphor body to have a substantially convex upper surface.
 12. Themethod of claim 7, wherein: the LED has an emission maximum within arange of about 420 nanometers to about 490 nanometers, the n-dopedsemiconductor body and the p-doped semiconductor body each including amember selected from the group consisting of gallium nitride,indium-gallium-nitride, gallium-aluminum-indium-nitride, and mixtures;and the phosphor has an emission maximum within a range of about 550nanometers to about 585 nanometers, the phosphor including acerium-doped yttrium-aluminum garnet, further including at least oneelement selected from the group consisting of yttrium, lutetium,selenium, lanthanum, gadolinium, samarium and terbium, and at least oneelement selected from the group consisting of aluminum, gallium andindium.